چکیده انگلیسی

Objectives
Though strategic deficits are extensively investigated in Parkinson's disease (PD), little is known about the effects of instruction for PD patients. Thus, we compared the ability to internally generate a cognitive strategy with the ability to use a strategy after elaborate strategy instruction.
Methods
Patients with PD (n = 14) and matched healthy controls (n = 22) were administered a Numerosity Judgement task in which they had to determine different numerosities of blocks presented in a square grid. In more complex task configurations, healthy participants tend to use a subtraction strategy. Participants in our study were confronted with a counting condition (A), a strategy initiation condition without instruction (B), and a strategy elaboration and strategy training condition (C).
Results
Patients and controls were comparable with respect to basic cognitive measures. PD patients and controls performed equivalently within the counting condition (A), but patients needed significantly more trials to initiate the subtraction strategy. With the exception of 1 PD patient, all patients were able to internally initiate the strategy (condition B). In condition C, both groups increased reaction times, but patients were significantly slower than controls. Moreover, only patients significantly increased error rates after strategy instruction.
Conclusion
As long as sufficient time is provided for solving the task, results do not show a general deficit in the ability to internally generate a cognitive strategy in PD. Failures in strategy utilization strongly depend on cognitive load (working memory, executive functions). This bears important implications for the neuropsychological rehabilitation of PD patients.

مقدمه انگلیسی

Deficits in executive cognitive functions affecting the ability to plan, monitor, and control goal-directed behaviour are one of the major characteristics of neuropsychological alterations in Parkinson's disease (PD) (e.g., Brown and Marsden, 1988, Dubois and Pillon, 1997, Mega and Cummings, 2001, Saint-Cyr, 2003 and Zgaljardic et al., 2003). These are usually attributed to the altered functional interactions between frontal cortex and basal ganglia due to the depletion of dopamine-producing neurons of the basal ganglia (e.g., Alexander et al., 1986, Cools, 2006, Cools, 2008, Lewis et al., 2003, Owen, 2004 and Price et al., 2009).
The inability to internally implement adequate cognitive strategies, especially in the absence of external guidelines, has been held responsible for a multitude of cognitive deficits in PD patients. Deficits in self-initiated strategy use leading to impaired performance in neuropsychological tests were, for example, seen in a spatial locomotor task (Leplow et al., 2002), in the Tower of London problem (e.g., Cools, 2006, McKinlay et al., 2008 and Owen, 2004), or in the utilization of semantic cues (Tweedy, Langer, & McDowell, 1982) and clustering strategies, respectively (e.g., Buytenhuis et al., 1994, Knoke et al., 1998, Taylor et al., 1990 and van Spaendonck et al., 1996). Also, deficits in spatial memory have been attributed to impaired strategic processing (Pillon et al., 1998). In addition, PD patients show deficits in other tests comprising a strategic component such as various aspects of intentional learning (e.g., Vingerhoets, Vermeule, & Santens, 2005), self-ordered pointing tasks (e.g., Gabrieli, Singh, Stebbins, & Goetz, 1996), conditional associative learning (e.g., Canavan et al., 1989, Gotham et al., 1988 and Pillon et al., 1998), problem solving (e.g., Kamei et al., 2008 and Morris et al., 1988), conscious decision-making (e.g., Brand et al., 2004), attentional set shifting (e.g., Williams-Gray, Hampshire, Barker, & Owen, 2008), or temporal ordering (e.g., Vriezen & Moscovitch, 1990). Thus, PD patients are typically impaired in the internal generation and initiation of effective cognitive strategies.
However, strategic deficits have not only been demonstrated within the laboratory. Inferior utilization of metacognitive memory strategies seems to induce problems of PD patients in real-life situations (Johnson, Pollard, Vernon, Tomes, & Jog, 2005). Even the increased risk of falls has been associated with a deficit in strategic behaviour (Bloem, Grimbergen, van Dijk, & Munneke, 2006).
Thus, one of the most fundamental deficits in PD is the inability to elaborate internally guided behaviour (e.g., Berger et al., 2004, Brown and Marsden, 1988, Brown and Marsden, 1990, Cools et al., 1984, Dubois and Pillon, 1997, Flowers and Robertson, 1985, Gabrieli et al., 1996, Jahanshahi et al., 1995, Norman and Shallice, 1986, Pollux, 2004, Taylor et al., 1986 and Werheid et al., 2007). Thus, the aspect of self-initiated, as opposed to externally triggered, cognitive behaviour seems to play an important role for cognitive performance in PD. Concordantly, PD patients regularly show difficulties in solving cognitive tasks which lack external guidelines and, consequently, necessitate the subjects to initiate and implement their own cognitive strategy.
On the other hand, strategy use following verbal instructions was less impaired. For example, Knoke et al. (1998) used the CVLT under three conditions of graded cueing. They demonstrated that PD patients show deficits in internally guided strategic behaviour leading to deficient verbal memory. However, patients benefited significantly from increasingly explicit cueing. In contrast, normal controls did not benefit from external cues. This was attributed to the fact that they were able to spontaneously and internally generate these cues themselves, i.e., showed optimal strategic behaviour without external cueing.
To date, this distinction between the internal initiation as well as the application of externally provided cognitive strategies in PD is not well understood. For example, it is unclear to what extent PD patients benefit from external strategy instruction. Moreover, strategic behaviour of PD patients has mainly been assessed via complex verbal memory paradigms, which might be problematic due to the limited working memory capacity of PD patients (e.g., Gabrieli et al., 1996).
Therefore, we compared the ability of PD patients to internally initiate a strategy with their ability to utilize an externally provided strategy in a simple Numerosity Judgement task. This paradigm requires subjects to determine different numerosities of blocks that are presented in a square grid. In tasks with a high number of presented blocks, healthy subjects often use the subtraction strategy, whereby the number of empty squares is subtracted from the total number of squares in the grid instead of counting the blocks (e.g., Luwel, Verschaffel, Onghena, & De Corte, 2003). We compared participants’ ability to internally initiate the subtraction strategy with the ability to implement the strategy after its external provision and elaborate strategy instruction. Our main predictions were (i) that PD patients would be especially impaired in the self-initiated strategy use and (ii) that strategy instruction would lead to enhanced performance, especially in PD patients.